I think the parent was referring to "lightweight task"-based concurrency like C#'s PLinq:

    // C# 
    int sum;
    Parallel.ForEach(myCollection, item => sum += item);

Which operates using a reasonably sized thread pool rather than a thread per item. Something similar in Rust (Excuse my rusty rust) would look like.

    let someList = ...
    parallel::for(someList.iter(), |item| {
       // Do thing with each item
    };

I think there is ongoing work on this topic, but it will likely only be library-level and not language-level (Just like Linq is a language level feature in C# but PLinq is a library). There are some third party crates that do this like simple_parallel.

Edit: Low-level simd exist as intrinsics and of course through llvm vectorizations.